This invention generally relates to projection systems including intrinsic polarizers. Specifically, the invention relates to transmissive or reflective projection systems including intrinsic polarizers.
Projection display systems usually include a source of light, illumination optics, an image-forming device, projection optics and a projection screen. The illumination optics collect light from a light source and direct it to one or more image-forming devices in a predetermined manner. The image-forming device(s), controlled by an electronically conditioned and processed video signal (typically digital), produces an image corresponding to the video signal. Projection optics then magnify the image and project it onto the projection screen. White light sources, such as arc lamps, in conjunction with color wheels have been used as light sources for projection display systems. However, recently, light emitting diodes (LEDs) were introduced as an alternative. Some advantages of LED light sources include longer lifetime, higher efficiency, superior thermal characteristics and better color gamut.
Examples of image-forming devices include liquid crystal panels, such as a liquid crystal on silicon device (LCOS). In liquid crystal panels, the alignment of the liquid crystal material is controlled incrementally (pixel-to-pixel) according to the data corresponding to a video signal. Depending on the alignment of the liquid crystal material, polarization of the incident light may be altered by the liquid crystal structure. Thus, with appropriate use of polarizers or polarizing beam splitters, dark and light regions may be created, which correspond to the input video data.
Another type of an image-forming device is a high temperature polysilicon liquid crystal device (HTPS-LCD). HTPS-LCD also includes a liquid crystal layer, in which the alignment can be controlled incrementally (pixel-to-pixel), as determined by the data corresponding to a video signal. The liquid crystal layer is sandwiched between two glass substrates, each with an array of transparent electrodes on them, thus being adapted for operation in transmission. Typically, at the corner of each HTPS-LCD pixel, there is a microscopic thin film transistor.
Current HTPS and LCOS based projection systems are enabled by the use dye-type polarizers. However, dye-type polarizers have limitations such as, for example, environmental instability, limited light transmission and/or degradation under high light flux.